#15 - Local, Must Be True

[Dave Killoran]

Complete Question Explanation
(The complete setup for this game can be found here: lsat/viewtopic.php?t=15971)

The correct answer choice is (E)

The question stem states that all of the nineteenth-century paintings are watercolors, which can be diagrammed as:


19 W


The contrapositive of this rule would be:

J97_Game_#3_#15_diagram 1.png

However, because of the two-value system, if a painting is not a watercolor then it must be an oil, and if a painting is not a nineteenth-century painting then it must be a twentieth-century painting. Thus, the contrapositive above can be more effectively diagrammed as:

O 20

Applying both of these statements to the original diagram leads to the following setup:

J97_Game_#3_#15_diagram 2.png

However, this does not take into account the second, third, and fifth rules. When those rules—which dictate what type of paintings are adjacent to each other—are taken into account, the diagram fills out considerably:

J97_Game_#3_#15_diagram 3.png

Painting 6 cannot be a nineteenth-century painting since that would violate the rule that states that a nineteenth-century painting must be next to or below another nineteenth-century painting. Thus, painting 6 is a twentieth-century painting, and answer choice (E) is correct.

[sarahlara]

Hello, I just wanted a little more clarification on this question. I was between D and E and did eventually pick the right answer of E. However, during my process of elimination, I ultimately chose E because I knew in spot 6 that a19th century watercolor painting could not go there. But answer choice D was appealing to me too because since it is a 20th century painting (as we know from the original set of rules in the game), so then it must be a oil painting correct? Painting 5 cannot be a watercolor painting and a 20th century painting in this question correct? I was just confused on the reasoning behind why D was incorrect if it must be true too? Please help thank you!!

[evelineliu]

Hi Sarah,

Painting #2 is 19th century, so it is a watercolor.
Painting #3 is an oil, so it is 20th century (contrapositive).
Painting #5 is 20th century. However, we cannot deduce that "if a painting is a 20, it is an oil."

Let's consider adjacency: Painting #2, a 19th century watercolor, has Painting #3, a 20th century oil, on its right. 20th century Painting #5 is below #2. Therefore, Painting #1 must be 19th century, and thanks to the question stem, a watercolor.

For (D), Painting #5 could be an oil, but it also could be a watercolor, which would force #4 to be watercolor as well.

Best,
Eveline